The answer to this question can be found in chapter 8. It is titled "Fizz Ed." Speak is broken up into four main sections, and each section coincides with a quarter at school. "Fizz Ed" is part of first quarter. By the time that this chapter rolls around, Melinda has been in school for a few weeks. The previous chapters have focused on some aspect of Melinda's school day. Readers get narration about teachers, English class, Spanish class, art class, and so on. Chapter 8 is about physical education class (gym class). Melinda thinks that PE should be illegal:

Gym should be illegal. It is humiliating.

Melinda explains a little bit about why she finds gym class humiliating. First, she is conscious of and embarrassed by her own body. Melinda doesn't see herself as very attractive, especially when she compares herself to Nicole; therefore, undressing in front of other girls is a very embarrassing process for Melinda. Additionally, Melinda isn't nearly as athletic as "jock" girls like Nicole. The descriptions of how dominating a force Nicole is on the athletic fields indicate to readers that Melinda finds it unfair that Nicole is so athletically talented and cute.

Nicole can do anything that involves a ball and a whistle. Basketball, softball, lacrosse, football, soccer, rugby. Anything. And she makes it look easy. Boys watch her to learn how to play better. It doesn't hurt that she's cute.